1. Field of the Invention
The present invention relates to a vehicle control technology for transmitting mechanical power received from an internal combustion engine through an engine output shaft, to driving wheels through a process of causing a transmission to change a rotational speed.
2. Description of the Related Art
A vehicle, in which mechanical power received from an internal combustion engine through an engine output shaft is transmitted to the driving wheels, typically has a transmission that transmits the mechanical power received through the engine output shaft to the driving wheels after a process of changing a rotational speed (namely, changing a torque). Examples of such a transmission include a continuously variable transmission (CVT) that can change gear ratios in a continuous manner and a geared transmission that changes a rotational speed by selectively using any one of a plurality of gears (gear ratios).
A vehicle equipped with such a transmission typically has a mode of operation (hereinafter referred to as an automatic mode) in which a gear ratio is automatically determined in accordance with an operational status of the vehicle. Such a vehicle also has another mode of operation (hereinafter referred to as a manual mode) in which any one of a plurality of predetermined gear ratios is selected in accordance with a driver's operation and thus the selected gear ratio is used to change a rotational speed in the transmission. Technologies for switching a mode of operation between the automatic and manual modes in accordance with the driver's operation have been proposed (see, for example, Japanese Patent (JP-B) Nos. 3656482 and 3218962).
JP-B No. 3656482 proposes that, at the time of switching a mode of operation from the automatic mode to the manual mode, a gear ratio (fixed gear ratio) in the manual mode immediately after the switching be set to a lower gear ratio than a gear ratio in the automatic mode immediately before the switching so that the rotational speed of a transmission input shaft (transmission input speed) is equal to or more than a predetermined level. Also, JP-B No. 3218962 proposes that, at the time of changing a mode of operation from the automatic mode to the manual mode, a gear ratio to be set in the manual mode be set at a level that is closest to and lower (or higher) than a gear ratio that has been set in the automatic mode.
In the technology described in JP-B No. 3218962, switching the automatic mode to the manual mode is accomplished when the driver shifts a select lever of transmission (shift lever) to a manual mode position from a “D” range position that puts the vehicle in the automatic mode (see FIG. 8 in JP-B No. 3218962) and moreover shifts the select lever of transmission to a “−” position that represents downshifting or a “+” position that represents upshifting.
Furthermore, Japanese Unexamined Patent Application Publication (JP-A) No. 11-257485 proposes a technology for switching an automatic mode to a temporary manual mode through the operation of a downshift switch or an upshift switch provided on a steering wheel without causing the driver to put the select lever of transmission in an “M” range position that puts the vehicle in a manual mode. JP-A No. 11-257485 describes a technology for, in a “temporary manual mode”, automatically switching a mode of operation from the temporary manual mode to the automatic mode after the passage of a “predetermined time” set in accordance with an operational status of the vehicle, such as a vehicle speed.
Manual modes include a mode in which a manual mode is terminated and switched to an automatic mode through a driver's operation, for example, driver's shifting of a select lever of transmission from an “M” range position for a manual mode to a “D” range position for the automatic mode, as described in JP-B No. 3218962, and a mode in which, following the operation of a switch provided on a steering wheel, the manual mode is automatically terminated and switched to the automatic mode in accordance with an operational status of the vehicle, as described in JP-A No. 11-257485. In other words, the manual modes include a “selective manual mode” in which a switch to the automatic mode takes place through an operator's predetermined operation and a “temporary manual mode” in which a switch to the automatic mode automatically takes place in accordance with the operational status of the vehicle.
The temporary manual mode is a mode in which, after the automatic mode is temporarily put in the manual mode, a switch to the automatic mode automatically takes place if the operational status of the vehicle meets a predetermined termination condition. For this reason, as compared to the selective manual mode, the temporary manual mode is often configured to make driver operations easier and at the same time more precisely reflect a driver's intention to accelerate or decelerate the vehicle. Accordingly, when the driver makes an attempt to switch a mode of operation from the automatic mode to the temporary manual mode by shifting gear ratios to lower ones through a paddle switch operation or a downshift operation, it is desirable to perform control in such a manner that the driver's intention to decelerate the vehicle is more precisely reflected in the gear ratios.